Question: Which of these numbers is prime? ${21,\ 24,\ 35,\ 41,\ 49}$
A prime number has exactly two factors: 1 and itself. The factors of 21 are 1, 3, 7, and 21. The factors of 24 are 1, 2, 3, 4, 6, 8, 12, and 24. The factors of 35 are 1, 5, 7, and 35. The factors of 41 are 1 and 41. The factors of 49 are 1, 7, and 49. Thus, 41 is a prime number.